The first few divisions in C elegans embryo has examples of both proliferative divisions in which both the daughters are equivalent, and differentiative divisions in which the daughters take on different fates. Studies are being undertaken of the dynamic properties of the cytoskeleton that are unique to differentiative divisions. In particular: factors are found to be segregated to one region of the cell prior to division; divisions are usually asymmetrical due to an asymmetry in the centrosomes of the mitotic apparatus; the mitotic apparatus is seen to align on a preformed axis of polarity. The purpose of this project is to use both in vivo imaging and correlative electron microscopy to study these phenomenon so as to gain insights as to the mechanisms used in the generationof cell diversity. The focus of this study is to elucidate the role of microtubules in positioning the spindle in early asymmetric cell divisions of Caenorhabditis elegans. We will use in vivo fluorescence microscopy to characterize the organization and dynamics of microtubules during spindle alignment in wildtype and mutant embryos. We are especially interested in mutants that exhibit alterations in the dynamic organization of microtubules in order to identify genes involved in spindle alignment. In addition, we will examine the ultrastructure of cortical microtubule attachment sites. Results will provide insight into the basic mechanisms and molecular components underlying cleavage plane specification in determinative cell divisions. SCXENTXFXC SUBPROJECT GRANT NUMBER: P41RR00570-27